Hydraulic cam shaft phase setters which are actuated by the engine lubricating oil pressure—hereinafter “phase setters”—have become widespread in motor vehicle construction, a preferred area of application for the invention, not least because of their reliable, robust design and favourable cost-benefit relationship. They do however have a certain design disadvantage over electromechanical phase setters, in that the adjusting speed is limited at low oil temperatures due to the limited oil pressure and high oil viscosity. In order to increase the adjusting speed in hydraulic phase setters, there is an endeavour to derestrict the flow cross-sections of the channels which guide oil to and in the phase setter. Alternatively or additionally, oil pressure storages and hydraulic designs are used in which, in order to rapidly adjust the rotational angular position of the cam shaft relative to the crankshaft, the unequal cam shaft torques are used to guide some of the oil from pressure chambers of the phase setter which are to be evacuated, directly—i.e. by bypassing the control valve—via reflux valves, into pressure chambers of the phase setter which are to be filled.
EP 2 463 486 B1, incorporated by reference herein, describes an advantageous design for a phase setter comprising a pressure storage. A direct oil flow between the pressure chambers of the phase setter, assisted by the cam shaft torque, is known for example from US 2005/0103297 A1, incorporated by reference herein.
The use of pressure storages is generally associated with a greater effort in construction. In the restricted construction spaces of modern drive motors, incorporating the pressure storage into the design causes significant problems. Using the cam shaft torques by directly connecting the pressure chambers which are to be evacuated to the pressure chambers which are to be filled requires a substantially greater effort in construction due to the additional connecting channels which have to be provided in the phase setter and the reflux valves which are arranged in said channels. The channel routing in the phase setter is complex. In accordance with the small construction size of the phase setters, the additionally required connecting channels can only be embodied with small flow cross-sections and/or a sharp flow deflection. The reflux valves required for controlling the direct oil flow produce additional pressure losses. The comparatively large number of reflux valves required increases the likelihood of components failing. A damaged or broken reflux valve makes it more difficult to set the phase angle and/or is associated with a substantial increase in the oil consumption of the phase setter, since a direct oil flow between pressure chambers which is enabled by a broken reflux valve has to be compensated for by constantly replenishing oil via the control valve of the phase setter. Because the pressure chambers which are to be evacuated are directly connected to the pressure chambers which are to be filled, it becomes more difficult to vent the phase setter for example after the engine is started.
In order to prevent oil from being able to flow from the pressurised pressure chambers back towards the oil supply system, reflux valves are arranged in the oil feed, upstream of the control valve of the phase setter. Preventing backflow through the feed is a prerequisite for high setting speeds and in particular low response times when phase adjustments are required. As described above with respect to the reflux valves provided at other locations, installing reflux valves does however increase the complexity of the phase setter and increases the flow resistance in the feed. Flutter valves are favourable with regard to the effort in construction and the flow resistance. For instance, valve structures which extend annularly around the rotational axis of the phase setter and comprise multiple spring tongues which are elastically flexible axially and arranged in a distribution in a circumferential direction are for example known from US 2016/0010516 A1 and WO 2017/088859 A1, which are incorporated by reference herein. In the phase setter of US 2016/0010516 A1, the valve structure and an annular filter disc are packed in between sheet-metal lamellae of a stack of lamellae. The stack of lamellae is fastened to a facing end of a rotor of the phase adjuster by means of pressure pins. The pressure pins serve to position the rotor on the facing end of a cam shaft. The stack of lamellae comprises many parts and is laborious to fit. The costs involved in providing and fitting the reflux valves are correspondingly high. In the phase setter of WO 2017/088859 A1, the valve structure is clamped between a stator ring and a stator cover and opens directly into the pressure chambers in order to equalise oil losses therein.